The family of synucleins is abundantly present in presynaptic neurons and is associated with numerous neurodegenerative disease states, collectively termed synucleinopathies. One member of this family, (-synuclein, is present as the major component of Lewy bodies [LB] in LB variant of Alzheimer's disease, dementia with LBs, sporadic Parkinson's disease, multiple system atrophy and neurodegeneration with brain iron accumulation. Mutants of alpha-synuclein, the A30P and A53T alpha-synucleins, are present in LBs of certain genetic forms of PD. However, neither the primary normal function of alpha-synuclein nor its mode of disease inducing action is known. Understanding the molecular and functional correlates of alpha-synuclein would help in the understanding of both the normative, and aberrant activity of this protein that give rise to the formation of fibrillary aggregates and LBs, in a process that is accelerated by increased oxidative stress and inflammation found in diseases of the aged. We provide preliminary evidence to suggest that one possible novel role for (-synuclein is to regulate the activity of the presynaptic dopamine transporter [DAT]. This regulation of DAT activity is bimodal, causing both the increased activity of the transporter and attenuation of normal transporter activity, as is indexed by [31H] dopamine uptake assays. The modulation of DAT function proceeds through rapid trafficking of the transporter to and from the plasma membrane. The mode of action of the A30P and A53T in such dual regulation of DAT activity differs from that of (-synuclein, and they also differ from one another in a highly prominent manner. In this proposal we will study in detail the mechanisms which underline such bimodal regulation of transporter activity, using cells co-transfected with alpha-synuclein and its subtypes, and the DAT cDNA, as well as in primary cultured neurons. The ability of the alpha-synuclein and its A30P and A53T mutants, and the identity of the structural components, which participate in direct protein:protein complex formation will be analyzed thoroughly in normal growth conditional states, through a battery of studies to include, immunology, transporter assays, immunocytochemistry and FRET. We will examine the role of oxidative stress in causing dysfunction of the three variants of alpha-synuclein. Studies will be conducted to determine if changes in alpha-synuclein/DAT interactions will reduce oxidative stress and cell death.